1. Field Of Invention
The invention relates to a highly active vanadium catalyst, and to a method for its production, which may be used in either a homogeneous or supported form for the polymerization of olefins to polyolefin having a narrow molecular weight distribution (MWD).
2. Background Information
The use of vanadium-based catalysts for the polymerization of olefins is well known. Early forms of vanadium catalysts were generally produced in oily or gummy forms which, to prevent reactor fouling, were useful only in high temperature solvent polymerization procedures wherein the product polyolefin was soluble in the polymerization solvent. To produce such vanadium catalysts in a form suitable for use in a slurry or gas phase polymerization reaction, it was necessary to deposit the vanadium catalysts on a support material. Although in heterogeneous supported form the vanadium catalyst could be used for the slurry or gas phase production of polyolefin directly in particle form in the reaction, the use of vanadium catalyst in supported form carried with it the consequence that the polyolefin product polymer would have a very broad molecular weight distribution (MWD). For very high molecular weight polyolefins the broad MWD characteristic is desirable, for certain applications, for instance when the polyolefin is intended for blow molding and extrusion applications. For other end use applications requiring a low to medium molecular weight polyolefin this broad MWD characteristic is undesirable because of the generation of an unacceptable amount of smoke during processing; for example, when a polyolefin of medium or low molecular weight is required for use in an application such as blow molding of household and industrial containers. As a consequence of its broad MWD, a medium or low molecular weight polymer contains a significant amount of low molecular weight (C.sub.10-32) oligomers which vaporize in blow molding processes to cause smoke.
Consequently, efforts in the art have been directed to the production of a high activity vanadium catalyst composition in solid form without the requirement of a catalyst support or alternatively to the production of a supported vanadium catalyst which will nevertheless produce a polyolefin of narrow MWD. Hence, U.S. Pat. No. 4,514,514 and U.S. Pat. No. 4,507,449 describe the production of a vanadium catalyst composition in solid form. This catalyst comprises a solid produced by the reaction of a vanadium compound, an organophosphorus compound, and a metal halide which precipitates to a solid form when an organoaluminum halide, particularly ethyl aluminum dichloride (EADC), is added. It is clear from the examples given in both patents that only a portion of the vanadium component precipitates from the reaction solution as a solid product. Likewise, EPO 86,481A describes a solid form of catalyst which may contain vanadium in addition to another transitional metal, principally titanium or zirconium, with a silicon compound which is then reacted with an organomagnesium compound to yield a solid product. Upon treating this solid product with EADC, a solid catalyst composition is formed.
In each of the above-described catalyst systems, to produce a solid reaction product it is necessary to employ either an organometallic compound, such as an organophosphorus or organomagnesium compound, to produce the final catalyst system or to use an organoaluminum halide, particularly EADC which either precipitates the catalyst in solid form from solution, or reduces a solid product to an active catalytic form.
It would be desirable to develop a vanadium-based catalyst for the polymerization of olefins to polyolefins of a narrow MWD which is soluble in hydrocarbons, which may be used in homogeneous or heterogeneous form, and which is highly active.